Unregulated urbanisation to blame for Chennai flooding: CSE experts

‘We have forgotten the art of drainage. We only see land for buildings, not for water’.

December 04, 2015 02:58 am | Updated November 16, 2021 04:00 pm IST - New Delhi:

Chennai is perhaps experiencing the worst impact of freak weather, but the city could have fared better had it protected and preserved its natural water bodies and drainage channels, experts at the Centre for Science and Environment (CSE) said on Thursday.

The unprecedented deluge that Chennai has been subjected to is a reminder of increasing frequency of such freak weather events across the Indian sub-continent, they said.

Speaking on the subject, CSE director-general Sunita Narain said: “We have repeatedly drawn attention to the fact that our urban sprawls such as Delhi, Kolkata, Mumbai, Chennai, Srinagar etc. have not paid adequate attention to the natural water bodies that exist in them. In Chennai, each of its lakes has a natural flood discharge channel which drains the spillover. But we have built over many of these water bodies, blocking the smooth flow of water. We have forgotten the art of drainage. We only see land for buildings, not for water.”

Waterbodies

CSE’s research shows that Chennai had more than 600 waterbodies in the 1980s, but a master plan published in 2008 said that only a fraction of the lakes could be found in a healthy condition. According to records of the State’s Water Resources Department, the area of 19 major lakes has shrunk from a total of 1,130 hectares (ha) in the 1980s to around 645 ha in the early 2000s, reducing their storage capacity. The drains that carry surplus water from tanks to other wetlands have also been encroached upon.

Stormwater drains The analysis also shows that the stormwater drains constructed to drain flood waters are clogged and require immediate desiltation. Chennai has only 855 km of stormwater drains against 2,847 km of urban roads. Thus, even a marginally heavy rainfall causes havoc in the city.

A number of cities including Chennai are both water-scarce as well as prone to flooding. Both problems are related — excessive construction leads to poor recharge of groundwater aquifers and blocking of natural drainage systems.

Sushmita Sengupta, deputy programme manager with CSE’s water team, said: “While Chennai has been struggling to meet its water needs and has been even desalinating seawater at a huge expense, it allowed its aquifers to get depleted.”

Chennai’s human-made drainage is no replacement for its natural drainage systems — a CSE analysis shows that there are natural canals and drains that directly connect the city with wetlands, waterbodies and rivers such as the Cooum and the Adyar that run through Chennai. The Cooum is supposed to collect surplus water from 75 tanks in its catchment area within the Chennai Metropolitan Area, while the Adyar is supposed to carry the surplus water of about 450 tanks in its catchment area and also from the Chembarambakkam tank (which is not in its catchment).

The rains in Chennai have broken a 100-year record (374 mm in just 24 hours). In November, the city had received 1,218 mm of rain, which was almost three times more than the average the city receives (407 mm).

A 2006 study by the Indian Institute of Tropical Meteorology (IITM) in Pune had said that extreme precipitation events were increasing in frequency and intensity in India during the period from 1950 to the 2000s.

CSE’s climate change experts say that while detailed attribution studies needed to be done to find out more links between the Chennai catastrophe and climate change, existing scientific studies do establish the possibility of a connection.

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